If you want quick, clean cuts in your metal project, then plasma arc cutting has to be at the top of your list.
But what type of gas does a plasma cutter use, and how does it work?
In this quick guide, we explore the four different types of gases suitable for plasma cutting.
Read on to learn the type of metal they are best suited to cut through and the advantages and shortcomings of each.
What Gas Does a Plasma Cutter Use?
Depending on the type of material and its thickness, different gases can achieve different quality of cuts.
Ideally, you’d want to have a good balance of results, speed, parts life, and operation cost.
Below are four of the most common gases a plasma cutter uses.
Compressed Air
It’s the most versatile of all plasma gases common for low current cutting, which produces top-quality cuts on mild and stainless steel as well as aluminum and carbon steel for plasma gouging.
Compressed air proves to be an economical choice since air is freely available. You’ll need a separate air compressor to run this setup, or, a plasma cutter with one built-in.
However, you will still need to remove any dust particles or moisture, which could scale expenses up a notch. It is most commonly used to cut through metals with a thickness of up to 1 inch.
Pros
- Tends to be economical
- Can be used for gouging too
Cons
- Leaves an oxidized cut area affecting weldability
- Oxidation and nitriding of the cut surface can occur, which can cause porosity in welds. You can combat this by using high-quality weld wire with denitrifiers and deoxidizers.
- Requires a separate air compressor unit
Oxygen
Using oxygen in your plasma torch offers the fastest cutting speed compared to any other plasma gas while still offering the best cut quality.
This gas is suitable for carbon steel with thicknesses of up to 1 -1/4 inch where the highest quality cuts are needed.
When oxygen plasma gas is used on carbon steel, they react to produce a fine spray of molten metal, with every droplet having low surface tension. This fine spray makes it easy to expel from the kerf.
When using oxygen plasma, the air acts as a shielding gas. Oxygen can also be used on stainless steel and aluminum, but it produces a rougher cut surface.
Pros
- Fastest cutting speed
- Best cut quality on mild steel
Cons
- Oxygen gas is expensive.
- The lifespan of the consumable parts is shorter. However, top-quality oxygen plasma torches use inert gases with oxygen plasma, like nitrogen, to get the same results.
That said, you can offset the high costs emanating from consumable parts and the gas itself by minimizing the expenses on post-welding operations, such as removing the dross and straightening beveled parts.
Nitrogen
Nitrogen is most suitable for high-current plasma cutters. It offers excellent cut quality for mild and stainless steel or aluminum up to 3 inches thick.
Nitrogen is usually used as a stabilizer with argon to add a wetting action to a weldment while keeping the cost down.
Nitrogen plasma works very well with CO2 as a secondary gas for better cutting speed and increased parts life compared to air. You can also use water as a secondary with a water table.
Pros
- Excellent cut quality.
- Enduring parts of life.
Cons
- Using CO2 costs way more than air and means using multiple gas cylinders to deliver sufficient flow that suffices that kind of need.
- Nitrogen gas is expensive.
Argon-Hydrogen
This particular mix is mostly used to cut through stainless steel and aluminum.
Argon-hydrogen produces a clean, straight cut, and very smooth surface on stainless steel.
The perfect stoichiometric ratio that provides optimal conditions is 65% argon and 35% hydrogen. This combination in that ratio offers the hottest plasma burning gas achieving near-perfect, clean cuts. For this reason, it’s not recommended to cut through mild steel.
Water injection torches use argon-hydrogen to cut stainless steel with gauges of up to 6 inches. It’s suitable for cutting any material above three inches thick.
Another advantage of using this combination is that it can also be used for plasma gouging on any material. However, you may find jagged dross along the bottom edge of the material, which sometimes can be annoying to work with.
As a form of countermeasure, nitrogen is used as a shielding gas with argon-hydrogen. This mixture of gas also tends to be expensive, raising the cost of operation.
Pros
- Produces the hottest plasma for cutting through materials.
- Can be used for plasma gouging on any material.
Cons
- Not economical due to the high-cost operation.
- Dross levels may occur along the bottom edge of the material being cut through.
Choosing The Right Gas
When it comes to choosing a gas to use for plasma cutting, you need to consider a few crucial factors, ranging from the kind of material you want to work on, the desired cut quality to your budget.
The table below serves to give a key to selecting the best gas to use for plasma cutting.
| Plasma Gas & Shield | Mild steel | Stainless | Aluminum |
|---|---|---|---|
| Air & Air | – Nice cut quality, – Faster cutting speed, – Cost-effective |
– Nice cut quality, – Faster cutting speed, – Cost-effective |
– Nice cut quality, – Faster cutting speed, – Cost-effective |
| Oxygen & Air | – Nice cut quality, – Faster cutting speed, – Very little dross |
– Not recommended | – Not recommended |
| Nitrogen & Air | – A little dross, – Fair cut quality, – Impressive parts life |
– Impressive parts life, – Good cut quality |
– Impressive parts life, – Excellent cut quality |
| Nitrogen & CO2 | – Little dross, – Impressive parts life, – Fair cut quality |
– Impressive parts life – Good cut quality |
– Impressive parts life – Good cut quality |
| Nitrogen & water | – A little dross, – Fair cut quality, – Impressive parts life |
– Excellent cut quality – Impressive parts life |
– Excellent cut quality – Impressive parts life |
| Argon-hydrogen & water | – Not recommended | – Perfect for thickness >1/2″ | – Perfect for thickness >1/2″ |
Related read: Best Plasma Cutter – Top picks & Reviews
Wrapping It Up
When it comes to plasma cutting, the general cut quality not only depends on the expertise of the welder but also the type of gas used.
Recommendations according to industry practice with regards to which gases work best for which materials are as follows:
- Oxygen plasma is best for mild steel where the air acts as a shielding gas, providing the best cut quality with the lowest dross. This gives little chance for rework while still retaining excellent weldability with high cutting speeds.
- Use argon-hydrogen paired with nitrogen as a secondary to get the best cut quality on aluminum and thick stainless steel. Ensure that your system is safe and compatible with argon-hydrogen gas.
- Use nitrogen plasma with CO2 to cut stainless and aluminum for the best results for the cost.
- For the most economical plasma cutting, clean compressed air is the best fit for cutting aluminum, mild and stainless steel.